TUBULATION OF ORGAN-FORMING AREAS 



481 



't' 



AREA 

 PE LLUCIDA 



AREA OPACA 



NEURAL TUBE 



■^ t^ * " EPIDERMAL TUBF— 7 



GUT TUBE ' 



NEURAL TUBE 



HEART RUDIMENT 



-. Y 



>y BLOOD ISLAN DS 



Fig. 233. Early body-form development in chick of 3 to 4 pairs of somites. (Approxi- 

 mately comparable to Hamburger and Hamilton, '51, stage 8, 26 to 29 hours of incu- 

 bation.) (A) Surface view, unstained specimen. (B) Stained, transparent preparation. 

 Observe blood islands in caudal part of blastoderm. (C) Median sagittal section. (D) 

 Same as (C), showing organ-forming layers. 



direction of the notochord is much more pronounced in the flattened blasto- 

 derms than in the rounded blastoderms of the frog, salamander, etc. (cf. 

 figs. 224; 237). {Note: Associated with the dorsal invagination of the roof 

 of the midgut in the frog, is the detachment of a median rod of entodermal 

 cells from the middorsal area of the gut. This median rod of cells comes to 

 lie between the notochord and the roof of the midgut. It is known as the 

 subnotochordal rod (fig. 225C). (See Chapter 15.) 



The development of the rudimentary hindgut is consummated by caudal 



